Met Éireann has issued a Status Yellow weather alert for heavy rain for Cork tomorrow.
Forecasters are warning of between 25mm and 40mm of rain will fall between 6am on Sunday morning and 5pm on Sunday evening.
Coastal areas are expected to be worse affected.
The weather may impact a number of major events taking place in Cork tomorrow.
The international Ironman competition is taking place in Youghal with thousands of athletes and spectators attending.
The Corpus Christi Eucharistic Procession is taking place through Cork city.
Kris Kristofferson is performing at the Marquee while Liam Gallagher plays at Musgrave Park tomorrow.
The Carnival of Science also continues at Fitzgerald's Park.
The weather has already seen the postponement of a planned regatta at Farran that was due to take place this weekend.